Guide wire extension

ABSTRACT

A guide wire system for use in catheter exchanges avoids the need for a separate exchange wire. Instead of the conventional practice in which the initial guide wire is removed and replaced with a longer exchange wire, a guide wire extension is attached to the proximal end of the initial guide wire thereby increasing its effective length so that it may be used to perform a catheter exchange. The initial guide wire remains in place in the patient&#39;s vasculature. The proximal end of the guide wire and the distal end of the exchange wire are formed to define a connection which may be crimped to effect the connection between the two wires. A crimping tool is provided to hold the mating ends of the guide wire and extension wire together while effecting the crimp.

This application is a continuation of application Ser. No. 766,8762,filed 9/18/85, now abandoned.

FIELD OF THE INVENTION

This invention relates to guide wires used in vascular catheterizationprocedures, and to techniques for performing catheter exchanges.

BACKGROUND OF THE INVENTION

In vascular catheterization procedures it often is necessary for thephysician to use different catheters in the diagnosis or treatment of aparticular blood vessel. For example, when performing a coronaryangiographic study, a physician commonly will use a series of catheters,to be inserted into the patient. Each of the catheters is provided witha different shape, size or configuration suited for a specific purpose.Angiographic studies typically include the use of at least three cardiaccatheters including a right coronary artery catheter, left coronaryartery catheter and a pigtail catheter. The three catheters each havedifferent shapes and configurations at their distal tips. The right andleft coronary artery catheters are shaped to facilitate placement oftheir distal outlet tips at the entries to the right and left coronaryarteries, respectively. The pigtail catheter is provided with a specialpigtail-shaped tip intended to reduce trauma as the catheter is advancedthrough the patient's tricuspid valve into the ventricle for ventricularstudies. By way of further example, other types of catheters may includeballoon dilatation catheters which are intended to be placed within astenosed portion of an artery and then inflated under high pressure toexpand the lumen of the artery so as to improve blood flow through theartery. In some dilatation procedures it may be desirable to use aseries of dilatation catheters having different sizes or balloonconfigurations.

It has long been common practice in the placement of catheters to use aguide wire which is placed in the patient's artery and which isreceivable in lumen of the catheter. With a guide wire in place, acatheter can be advanced over the guide wire and thereby guided to theintended vascular site. The guide wire serves to center the catheterwithin the blood vessel and reduces the risk of trauma to the bloodvessel by the advancing catheter. The use of a guide wire reduces therisk that the distal end of the catheter might become caught o the innersurface of the blood vessel lumen. The use of a guide wire also enablesthe catheter to be advanced through the blood vessel relatively quickly,thereby reducing the time required for the procedure.

A standard guide wire typically is slightly longer than the catheterwith which it is to be used. For example, with an angiographic catheterof the order of 130 centimeters long, the guide wire typically may be ofthe order of 145-175 centimeters long. When the catheter is in placeover the guide wire, a relatively short portion of the guide wireprotrude proximally from the catheter. That enables the guide wire to bemanipulated, if desired, from its proximal, protruding end. In thatregard, it may be noted that the guide wire may be a steerableconstruction in which a bend is formed in its distal tip and thedirection in which the bent distal tip extends it controlled by rotatingthe guide wire from its proximal end. For example, the guide wire may beof the type described in U.S. Pat. application Ser. No. 421,315 filedSept. 22, 1982.

When it is necessary to change catheters, it usually is preferred thatthe catheter be removed in a manner which enables a guide wire to remainin place in the blood vessel so that the next succeeding catheter in theprocedure can be inserted into the blood vessel, over the guide wire,and will be guided to the intended site in the blood vessel. In order tomaintain a guide wire in place while withdrawing the catheter, the guidewire must be gripped at its proximal end to prevent it from being pulledout of the blood vessel together with the catheter. The catheter,however, is longer than the proximal portion of the guide wire whichprotrudes out of the patient. Thus, before the catheter is fullywithdrawn it completely covers the proximally extending end of the guidewire. As a result, there is no means by which a standard guide wire canbe held in place to prevent it from being withdrawn together with thecatheter If, as is often the case, it is desired to place the nextsucceeding catheter by advancing it over a guidewire, a new, longerguide wire is inserted in to the blood vessel and advanced into aposition to provide a guide for the next catheter.

It is recognized generally as undesirable to insert, advance andwithdraw a series of guide wires through a patient's blood vessels. Todo so greatly increases the risk of trauma and puncture to the patientand also extends the duration of the procedure. It also requiresexposure of the patient to additional radiation because of theadditional fluoroscopy which would be required to place the successiveguide wires. In order to reduce the risk of puncture or trauma it hasbecome a long time practice to use an exchange wire when performingcatheter exchanges. The exchange wire typically is about 300 centimeterslong, much longer than the typical standard guide wire. The structure ofthe standard and exchange wires typically is the same except for thelength. The additional length of the exchange wire results in a longproximally protruding portion which is longer than the catheter to beremoved. When a catheter is removed some part of the proximallyextending portion of the exchange wire will always be exposed to providea means by which the exchange wire ca be gripped and its position in theblood vessel maintained. Use of the exchange wire reduces the risk oftrauma to the patient because it is placed while the first catheterremains in the patient. Thus, the procedure involves initially, removalof the standard guide wire from the catheter while the catheter remainsin place in the patient. Then the exchange wire is advanced through thecatheter to replace the original guide wire. Because the exchange wireis guided through the patient's blood vessel by the first catheter, itdoes not contact the lumen of the blood vessel except, perhaps, for asmall portion which protruded distally of the first catheter. Theoriginal catheter then is withdrawn over the exchange wire, which ismaintained in place in the blood vessel. The next succeeding catheterthen can be inserted into the patient over the exchange wire.

The foregoing system and technique of using a long exchange wire hasbeen conventional practice for many years. The use of an exchange wireduring catheter exchanges, however, is not free from difficulty. Theproximally extending end of the exchange wire is quite long and cannotbe manipulated easily, should it be desired to manipulate the distal endof the exchange wire. Additionally, the placement of the exchange wiremust be performed under fluoroscopy to assure that it is placed properlyin the patient's blood vessel. The use of an exchange wire also adds tothe time and the complexity of the procedure. Notwithstanding thesedifficulties, the use of exchange wires has continued to be commonpractice in making catheter exchanges.

It is among the general objects of the invention to provide an improvedguide wire system and technique by which catheter exchanges can beperformed without the use of separate exchange wire and in a mannerwhich avoids the foregoing and other difficulties.

SUMMARY OF THE INVENTION

The present invention enables a catheter exchange to be made withoutrequiring any guide wire exchanges. In accordance with the presentinvention a guide wire extension is attached to the proximally extendingend of the guide wire while the guide wire remains in place in thepatient. The guide wire extension effectively increases the length ofthe guide wire. After the extension is attached to the guide wire, thecatheter can be withdrawn over the guide wire and its extension. Theextended length enables the proximal end of the combined guide wire andextension to be exposed at all times so that its position can bemaintained during removal of the catheter. Once the first catheter hasbeen removed, the new catheter can be inserted over the combined guidewire and extension. The technique substantially shortens the duration ofthe procedure because the extension can be attached to the proximal endof the guide wire much faster than a conventional wire exchange can beperformed. Additionally, there is a further reduction in risk ofpuncturing the blood vessel. There also is less exposure to fluoroscopicradiation which is required each time a guide wire is inserted.

In accordance with the invention the proximal end of the guide wireincludes a connector arrangement which may be in the form of a tubularsocket. The socket is receptive to a mating tip formed at the distal endof the extension wire. When the extension wire and guide wire are mated,the joint is secured, as by crimping with a special crimping tool. Inthe preferred embodiment, the crimp is a trapezoidal shape and is formedto have a low profile so that it will not adversely interfere with theadvancement of the catheters over the crimped joint. After a successfulcatheter exchange, the joint can be broken to separate the extension toallow for easy manipulation of the guide wire, from its proximal end.

It is among the objects of the invention to provide a new and improvedtechnique for performing catheter exchanges.

Another object of the invention is to provide a guide wire system whichenables catheter exchanges to be performed without the use of anexchange wire.

Another object of the invention is to provide a technique for performingcatheter exchange which is quick and requires no fluoroscopic exposure.

A further object of the invention is t provide method and apparatus forattaching an extension on to the proximal end of the guide wire whilethe guide wire is in place thereby to facilitate catheter exchanges overthe combined guide wire extension.

Another object of the invention is to provide a system of the typedescribed in which the extension wire can be separated from the guidewire after the catheter exchange has been completed.

DESCRIPTION OF THE DRAWING

The foregoing and other objects and advantages of the invention will beappreciated more fully from the following further description thereof,with reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic illustration of a patient undergoingcatheterization with a catheter inserted percutaneously into the femoralartery and showing, diagrammatically, the catheter and guide wire whichprotrude proximally, and illustrating further, in phantom, the relativelength of an exchange wire;

FIG. 2 is a composite fragmented and partly sectional unscaledillustration of the proximal end of a guide wire of conventional lengthin accordance with the present invention and the guide wire extension,showing the distal end of the extension aligned with the proximal end ofthe guide wire in readiness to be mated;

FIG. 3 is an unscaled illustration of the proximal and distal ends ofthe guide wire and extension wire of the invention when mated but beforebeing crimped;

FIG. 4 is an unscaled illustration of the crimped connection of theguide wire an extension wire;

FIG. 5 is a partly fragmented and partly sectioned illustration of thecrimping tool;

FIG. 6 is a side elevation of the jaw end of the crimping tool with thejaws closed to a wire gripping position;

FIG. 7 is a sectional illustration as seen along the line 7--7 of FIG. 6illustrating the jaws gripping the proximal end of the guide wire inreadiness to receive the guide wire extension;

FIG. 8 is an illustration similar to FIG. 7 with the extension wire andguide wire connected and with the jaws of the crimping tool in a crimpedconfiguration; and

FIG. 9 is a side elevation of the jaws of the crimping tool in crimpedconfiguration as seen along the line 9--9 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates, in highly diagrammatic form, the catheter 10 andguide wire 12 which have been inserted into the patient's femoral arteryand have been advanced to the region of the patient's heart where thedesired procedure will be performed. The guide wire 12 and catheter 10will have been inserted and placed in the artery in accordance with wellknown procedures.

When it is desired to exchange the catheter for another, it is importantthat the guide wire be maintained within the patient's artery so that itmay guide the next succeeding catheter quickly and efficiently to theintended site in the patient's vascular system. Typically, theclearances between the guide wire 12 and inner lumen of the catheter 10,coupled with the bends which the catheter 10 and guide wire 12 mustfollow along the patient's vascular system are such that withdrawal ofthe catheter 10 tends to drag the guide wire 12 out with the catheter10. In order to maintain the guide wire 12 in place while the catheter10 is withdrawn, it is necessary to hold the guide wire 12 by itsproximal end 16 while withdrawing the catheter 10 over the guide wire12. Because the proximal end 16 of a conventional guide wire onlyextends proximally beyond the proximal end 18 of the catheter by anamount which is substantially less than the length of the catheter 10,there is no means for retaining the conventional guide wire 12 inposition while the catheter 10 is removed.

In order to effect a catheter change, it has been the practice for manyyears to use an exchange wire. The exchange wire is substantially longerthan the conventional length of guide wire 12 and may be of the order of300 cm long. The additional effective length of the exchange wire ascompared to the conventional length guide wire 12 is represented by thephantom line 20 in FIG. 1. The length of the exchange wire is such thatits tip, represented by the reference character 22, is spaced from theproximal end 18 of the catheter by a distance which is greater than thelength of the catheter 10.

In performing the exchange, the guide wire 12 is removed from thecatheter 10 while the catheter 10 remains in the patient. The exchangewire then is inserted into and advanced along the catheter 10 until itsdistal tip is located at the intended site within the patient's vascularsystem. The additional length of the exchange wire which protrudesproximally of the proximal end 18 of the catheter 10 provides asufficiently long means by which the exchange wire may be gripped sothat its position may be maintained in the patient while the catheter 10is withdrawn. Thus, the catheter 10 may be withdrawn over the exchangewire, and the next catheter may be placed in the patient by advancing itover and along the exchange wire. After the next catheter has beenplaced, it may be desirable to remove the exchange wire and replace itwith another standard length guide wire, depending on the type ofcatheterization procedure which is to be performed. For example, if theprocedure requires use of a steerable guide wire which must bemanipulated from its proximal end, such a guide wire will have to beexchanged for the exchange wire after the catheter exchange has beenmade.

In accordance with the present invention, catheters may be exchangedwithout requiring removal of the guide wire 12 and without requiring theinvolvement attendant to the use of an exchange wire. The guide wire 12is connected, at its proximal end, to an extension wire 24 while theguide wire 12 and catheter 10 remain in the patient. The extension wire24 is attached securely to the proximal end of the guide wire 12 andserves to extend the effective length of the guide wire 12 sufficientlyto permit the catheter 10 to be withdrawn over the guide wire 12 andextension 24.

As shown in FIG. 2, the guide wire 12 is provided with a hollow tubularconnective fitting 26 which is attached to and extends proximally of theproximal end of the guide wire 12. In the illustrative embodiment, theguide wire 12 is illustrated as having a proximal end formed from asolid wire such as the type of guide wire illustrated in theaforementioned U.S. Pat. application Ser. No. 421,315. It should beunderstood, however, that the general principles of the presentinvention may be applied to any guide wire by modifying the proximal endof the guide wire to include a means for attaching the proximal end ofthe guide wire to an extension wire.

In the illustrative embodiment, the proximal end of the guide wire isprovided with a reduced diameter projection 28 which is received withinan end of the tube which forms the connective fitting 26. The tube 26 issecured to the guide wire 12 such as by brazing as indicated at 30 atthe junction of the end of the tube 26 with the shoulder 32 defined atthe transition of the guide wire 12 to the reduced diameter projection28. Alternate construction may have tapered portion to form thetransition from the guide wire to the projection 28. The outer diameterof the tube 26 preferably is the same as the outer diameter of the guidewire 12. The tube 26 thus defines an elongated socket 34 which isreceptive, as will be described, to the distal end of the extension wire24. The tube 26 may be formed from stainless steel, as may be the guidewire 12. The tube 26 may be fabricated from readily available hypodermictubing. The wall thickness of the tube 26 should be selected so that itcan be crimped easily, as will be described, but it also must be capableof providing sufficient rigidity to maintain a secure connection to theguide wire extension 24. By way of dimensional example, with a guidewire of the type described in the aforementioned U.S. Pat. applicationSer. No. 421,315, the proximal end of the guide wire may have an outerdiameter of the order of 0.016 inches and the tubing 26 will have thesame outer diameter. A wall thickness for the tubing of the order of0.0015 to about 0.003 inches has been found to be satisfactory. Thelength of the tubing 26 may be of the order of about four inches and thesocket may be of the order of about three inches deep.

The guide wire extension 24 also may be formed from stainless steel andpreferably is of comparable diameter t that of the guide wire 12 andextension 26. The distal end of the extension 24 has a reduced diametertip 36 which is insertable into the socket 34 of the fitting 26. Theguide wire extension 24 may be provided with a tapered transition region38 between its main body and the tip 36. By way of dimensional example,in the illustrative embodiment, the tip 36 may be of the order of aboutfour cm long having an outer diameter of 0.008-0.009 inches so that itmay be received within the socket 34. The tip 36 and socket 34 should besufficiently long so that the full length of the tip 36 extends into thesocket 34.

FIG. 3 illustrates the manner in which the guide wire 12 and guide wireextension 24 mate. The distal tip of the extension simply is insertedinto the socket 34 of the fitting 26. The connected members then aredeformed, preferably in a configuration illustrated in FIG. 4, to securethe wire 12 and extension 24 together. Once secured, the effectivelength of the wire 12 will have been extended and the catheter 10 can beremoved over the combined effected extended length without requiringremoval of the guide wire 12.

The mechanical attachment is effected preferably by deforming theconnected tube 26 and tip 36 by displacing a segment of them laterallyof the common axis X of the combined guide wire 12 and extension 24 inwhat may be considered as a generally U-shaped configuration. The extentof lateral displacement, however, is limited by the flexibility of thecatheters with which the device is to be used. The extent of lateraldisplacement should not be so great or sharp so as to require so sharp abend in the catheter that it will interfere with smooth advancement ofthe catheter 10 over the point. In accordance with the presentinvention, it has been found that a trapezoidal shaped deformation seemsto provide the best results, although other non-trapezoidal shapes mightbe employed. As shown in FIG. 4, the preferred shape of the crimpincludes a central segment 40 and a pair of spaced segments 42 which areformed between the ends of the tube 26. Preferably the crimp is formedin a manner which leaves a short proximal segment 44 of the tubing 26which remains in coaxial alignment with the extension wire 24. In thepreferred embodiment, the spaced segments 42 are arranged at an angle Aof about 30° to the central axis of the guide wire 12 and extension 24.The central crimped segment 42 is displaced transversely of the axis Xbut extends substantially parallel to it. Preferably, the centralsegment 40 can be displaced about 0.060 inches from the common axis X.The overall length of the crimp including the end segments 42 andcentral segments is of the order of about 0.60 inches.

It has been found that such a connection can be made quickly and easily.It maintains sufficient tensile strength of the order of about one totwo pounds force so as not to come apart during use, yet it does notinterfere with advancement of the catheter as it is snaked over thecrimped portion. Additionally, it should be noted that the connectionalso maintains sufficient compressive strength so that when the catheteris advanced over the guide wire and extension, the connection betweenthe guide wire and guide wire extension will not collapse or otherwisebecome adversely deformed as a result of the compressive force resultingfrom pushing the catheter along the guide wire extension. Additionally,the connection may be broken easily and quickly should it be desired toseparate the guide wire extension 24 from the guide wire 12. The guidewire 12, fitting 26 and guide wire extension 24 preferably all arecoated with a thin film of low-friction material such aspolytetrafluoroethylene to enhance the ease with which the catheter mayslide over the guide wire and connected extension.

Although the principles of the invention may be applied to a wide rangeof sizes of guide wires and catheters, the configuration in theillustrative embodiment is useful particularly with smaller diameterguide wires for use with relatively small diameter flexible catheters.For example, the illustrative embodiment of the invention isparticularly advantageous when used with guide wires of the order of0.025 diameter and smaller which, in turn, may be used with catheters ofthe order of 6 French and smaller.

The invention also provides a device for facilitating connection andcrimping of the connected guide wire 12 and extension wire 24. As shownin FIGS. 5-9, the crimping device indicated generally at 50 may bemolded from a suitable plastic such as for example, Delrin (trade namefor acetal). The crimping device 50 is somewhat in the form of pliershaving a pair of handle members 52, 54 which are connected to each otherat a pivot pin 56 and slot 58 formed integrally with the members 52, 54.The members 52, 54 thus are pivotable with respect to each other anddefine a pair of jaw members 60, 62 which are movable toward and awayfrom each other. The jaws 60, 62 are arranged to hold the connectivefitting 26 at the proximal end of the guide wire 12 in a position toreceive the tip 36 of the extension wire 24. The jaws 60, 62 alsoinclude an arrangement for guiding the tip 56 of the extension wire 24into the socket 34 of the fitting 26 and, when the extension wire andfitting 26 are mated, for effecting the crimp illustrated in FIG. 4.

One of the jaw members 60 has an inner face 64. The jaw 60 is molded toinclude a platform 66 which extends away from the jaw face 64. Theplatform is of trapezoidal configuration and includes an upper face 68which is parallel to the inner face 64 of the jaw 60, and a pair ofsloping side faces 70. The transversely extending groove 72 is formedtransversely along the upper face 68 of the platform 66. The groove 72is intended to receive and cooperate in holding the connective fitting26. The opposing jaw 62 is formed with a trapezoidal shaped indentation74 having surfaces corresponding to and paralleling those of theplatform 66, including surfaces 70 and 72. The jaw member 62 alsoincludes a pair of transversely extending members 76, 78 which havesurfaces 80, 82. The surfaces 80, 82 extend parallel to the surface 64of member 52 when the jaws 60, 62 are mated. As will be described infurther detail, the fitting 26 may be positioned in the device byplacing it along the channel 72 and then closing the jaw 62 to cause jawsurfaces 80 and 82 to engage the fitting 26 and hold it in place, readyto receive the tip 36 of the extension wire 24. The surface 82 of thejaw member 62 is provided with a transversely extending groove 84 whichreceives the end of the fitting 26 in a manner and for a purpose whichwill be described. The outer end of the groove 84 is formed to includean upwardly and transversely diverging funnel-shaped channel 86.

The jaw end of the handle member 52 includes an integrally formedelongate finger 88 which is separated from the main portion of the jawmember 60 by a slot 90. The finger is formed so that it may flex andbend with respect to the jaw 60 and handle 52. The outer end of thefinger 88 is formed to include a platform 92 having an upper surface 94.The platform 92 includes a transversely extending groove 96 whichcommunicates with transversely opening funnel-shaped channel 98. Theplatform 92 is located with respect to the transverse portion 78 of thejaw 62 so that when the jaws 60, 62 are brought together, the surfaces82 and 94 will butt against each other with the grooves 84, 96cooperating to define a guiding passage and the channels 86, 98cooperating to define a funnel leading into the guiding passage.

As shown in FIGS. 6 and 7 the connective fitting 26 is held between thejaws 60, 62 with the fitting 26 being engaged by the channel 72 on theplatform 66 and by the surfaces 80 and groove 84 of the jaw member 62.The fitting 26 thus is held securely and its socket 34 is in alignmentwith the guiding passage defined by the cooperating grooves 84, 96. Thedistal tip 36 of the extension wire 24 then may be passed through thefunnel 86 and into the aligned socket 34. The funnel defined by thechannels 86, 98 serves to facilitate entry of the tip 36 into the socket34.

Once the distal tip 36 of the extension wire has been inserted throughthe funnel and guiding passage into the socket 34, the crimping tool isoperated to draw the jaws 60, 62 together and effect the crimpingoperation. During the crimping operation, the finger 88 flexesdownwardly as shown in FIG. 7 to maintain the axial alignment of theguide wire 12 and extension wire 24 which are located proximally anddistally of the crimp. After the crimp has been completed, the jaws 60,62 are opened to release the connected wires 12, 24. The guide wire 12thus has been effectively extended so that the catheter 10 may beremoved without requiring withdrawal of the guide wire 12 and insertionof a new exchange wire. After the extension has been attached and thecatheter has been withdrawn, the next succeeding catheter is advancedover the extension and the guide wire into and through the patient'sblood vessel. Depending on the technique involved and the physician'spreference, the extension may be permitted to remain attached to theguide wire or may be separated easily. Separation can be effected bycutting the guide wire distally of the crimp.

From the foregoing, it will be appreciated that the invention provides atechnique and devices by which catheter exchanges may be made in amanner which shortens the time required for the procedure, reduces theamount of radiation exposure to the patient and reduces further the riskof trauma to the patient. It should be understood, however, that theforegoing description of the invention is intended merely to beillustrative thereof and other embodiments and modifications may beapparent to those skilled in the art without departing from its spirit.

Having thus described the invention, what I desire to claim and secureby Letters Patent is:
 1. A guide wire system for guiding an elongate,flexible catheter having a guide wire lumen through a lumen in the bodyof a patient and adapted to facilitate exchange of the catheter foranother catheter comprising:a guide wire having a proximal and a distalend; an extension wire having a proximal end and a distal end; tubularconnector means on at least one of said wires for connection of theproximal end of the guide wire with the distal end of the extension wirethereby to extend the effective length of the guide wire; said tubularconnector means being constructed and arranged to be received within thecatheter lumen and to have a low profile in which its cross-sectionaldimensions are substantially the same as those of the wire to enable thecatheter to be passed over the wires and the connector means when thewires are connected by the connector means; whereby a catheter placed ina patient and having the guide wire extending therethrough may beexchanged for another catheter by connecting the proximal end of theguide wire with the distal end of the extension wire, then removing thecatheter over the connected wires and then advancing another catheteronto and along the wires without requiring removal or substantial changeof position of the guide wire.
 2. A guide wire system as defined inclaim 1 further comprising, in combination, a flexible catheter throughwhich the guide wire and extension wire are slidably received, andwherein the combined length of the guide wire and the extension wire isapproximately twice the length of the catheter.
 3. A guide wire systemas defined in claim 1 wherein the tubular connector means comprisesmeans for effecting a mechanical interlock between the proximal end ofthe guide wire and the distal end of the extension wire.
 4. A guide wiresystem as defined in claim 3 further comprising:said mechanicalinterlock being constructed and arranged so as to have a tensilestrength sufficient to withstand axial separation force of the order ofone pound.
 5. A guide wire system as defined in claim 4 furthercomprising:said mechanical interlock being constructed and arranged soas to have a compressive strength sufficient to withstand an axial loadof the order of one pound.
 6. A guide wire system as defined in claim 3wherein said mechanical interlock comprises a crimped interlock.
 7. Aguide wire system as defined in claim 3 further comprising:saidmechanical interlock being constructed and arranged so as to have acompressive strength sufficient to withstand an axial load of the orderof one pound.
 8. A guide wire system as defined in claim 3 wherein themechanical interlock further comprises:a tubular socket formed on one ofthe proximal ends of the guide wire or distal end of the extension wire,the other of said ends of the guide wire and extension wire beingdimensioned to be received within the tubular socket thereby to matesaid other end and tubular socket; said received other end and tubularsocket being adapted to be formed transversely into a generally U-shapedconfiguration.
 9. A guide wire system as defined in claim 8 wherein thetubular socket is formed on the proximal end of the guide wire and thedistal end of the extension wire is dimensioned to be received withinthe tubular socket.
 10. A guide wire system as defined in claim 9further comprising;the distal end of the extension wire being taperedand terminated in a substantially uniform diameter elongate tip adaptedto be received within the tubular socket of the guide wire.
 11. A guidewire system as defined in claim 10 wherein the extension wire is a solidrod.
 12. A guide wire system as defined in claim 9 furthercomprising:the tubular socket being in the form of a thin walled tube ofthe order of four inches long, having a wall thickness of between about0.0015 and 0.003 inches, the socket in the tube being of the order ofthree inches deep.
 13. A guide wire system as defined in claim 8 whereinthe outside dimensions of the tubular socket are the same as those ofthe portion of the guide wire adjacent to the tubular socket.
 14. Aguide wire system as defined in claim 3 wherein the mechanical interlockfurther comprises:a tubular socket formed on the proximal end of theguide wire, the distal end of the extension wire defining a mated endand being dimensioned to be received within the tubular socket; themated end and tubular socket being deformed transversely int a generallytrapezoidally-shaped portion having a central segment and a pair ofsloped end segments.
 15. A guide wire system as defined in claim 14wherein said guide wire and extension wire extend along an axis andwherein said sloped segments extend at an angle of about 30° to saidaxis.
 16. A guide wire system as defined in claim 14 wherein the guidewire and extension wire extend along an axis and wherein the centralsegment is displaced from the axis by an amount sufficient to retain theguide wire and extension wire together when subjected to a force of atleast about one pound.
 17. A guide wire system as defined in claim 16wherein the central segment is displaced from the axis by about 0.06inches.
 18. A guide wire system as defined in claim 17 wherein theoverall length of the trapezoidally-shaped portion is approximately 0.60inches.
 19. A guide wire system as defined in claim 1 wherein said bodylumen comprises a blood vessel.
 20. A guide wire system as defined inclaim 1 wherein said guide wire is round in cross section.
 21. A guidewire system as defined in claim 1 further comprising, in combination, aflexible catheter, and wherein the guide wire is longer than thecatheter.
 22. A guide wire system for guiding an elongate, flexiblecatheter having a guide wire lumen through a lumen in the body of apatient comprising:a guide wire having a proximal end and a distal end;an extension wire having a proximal end and a distal end; tubularconnector means for connection of the proximal end of the guidewire withthe distal end of the extension wire, thereby to extend the effectivelength of the guide wire; said guide wire being rounded incross-section; said connector means being round in cross-section andhaving a diameter no greater than that of the guide wire thereby toenable the catheter to be passed over the wires and the connector meanswhen the wires are connected by the connector means; whereby a catheterplaced in a patient and having the guide wire extending therethrough maybe exchanged for another catheter by connecting the proximal end of theguide wire with the distal end of the extension wire, then removing thecatheter over the connected wires and then advancing another catheteronto and along the wires without requiring removal of substantial changeof position of the guide wire.
 23. A guide wire and catheter systemcomprising:an elongate flexible catheter having a guide wire lumen; aguide wire having a proximal end and a distal end and being receivablein the guide wire lumen of the catheter, the guide wire being longerthan the catheter; an extension wire having a proximal end and a distalend; tubular connector means for connection of the proximal end of theguide wire with the distal end of the extension wire thereby to extendthe effective length of the guide wire; said tubular connector meansbeing constructed and arranged to be received within the catheter lumenand to enable the catheter to be passed over the wires and the connectormeans when the wires are connected by the connector means; whereby acatheter placed in a patient and having the guide wire extendingtherethrough may be exchanged for another catheter by connecting theproximal end of the guide wire with the distal end of the extensionwire, then removing the catheter over the connected wires and thenadvancing another catheter onto and along the wires without requiringremoval of substantial change of position of the guide wire.
 24. In aguide wire system for guiding an elongate, flexible catheter having aguide wire lumen through a lumen in the body of the patient, said systemhaving a guide wire having proximal and distal ends, the improvementcomprising:an extension wire having a proximal end and a distal end;connector means on at least one of said wires for connecting theproximal end of the guide wire with the distal end of the extension wirethereby to extend the effective length of the guide wire; said connectormeans being constructed and arranged to be received within the catheterlumen and to have a low profile in which its cross-sectional dimensionsare substantially the same as those of the wires to enable the catheterto be passed over the wires and the connector means when the wires areconnected by the connector means; whereby a catheter placed in a patientand having the guide wire extending therethrough may be exchanged foranother catheter by connecting the proximal end of the guide wire withthe distal end of the extension wire, then removing the catheter overthe connected wires and then advancing another catheter onto and alongthe wires without requiring removal or substantial change of position ofthe guide wire.